Did my DC powerpack corrupt my locomotive?

[jbrock27]

"Files" (at least the one I see which is to the left of "About") is grayed out and nothing happens when clicking on it.

[zeeglen]

"Files" (at least the one I see which is to the left of "About") is grayed out and nothing happens when clicking on it.

Try the other website Locomotive Maintenance, that one does not need moderator approval for membership.

[jbrock27]

It is the same thing there bro.

[zeeglen]

It is the same thing there bro.

Not sure why, they work for me but then I am the moderator.
Do you have a yahoo account?  Maybe yahoo denies access to groups unless you register on yahoo first.
Do you know if there is any way to attach this file here?  When I try I get a message something like "Upload buffer full" and the file is only 110KB so should work.  The pics are embedded in the Word file and I don't think I can extract them, and as I said the originals are lost.

[zeeglen]

MRC1370 Manufacturing Defect and Solution



Above: The yellow trace is a MRC1400 working properly at low speed and outputting mostly half-wave rectified with low voltage pulses in the gaps between the main higher voltage pulses.  As the throttle is advanced both the low and higher voltage pulses increase, but the low voltage pulses increase faster until at full speed all pulses are the same voltage, ie full-wave rectified.  The half-wave causes the motor to generate higher torque at low speed.
The blue trace is the MRC1370 with the manufacturing defect.  It outputs full-wave at all voltage (speed) levels.  With the fix shown below it will instead perform like the MRC1400 (and others) as intended.

Above is the MRC1370 schematic showing where the missing R1 is connected in error.  Install a 5% 5600 ohm 1/4 watt resistor at the missing R1 location.  Either cut the trace where shown or lift that lead of the new R1 out of the pcb and connect instead to the diodes AC input (transformer secondary).  Which wire of the transformer secondary is usually not important unless you run more than one power pack on the same train and need to have all phased the same way.  Use oscilloscope or experiment with phase to ensure locos do not speed up when straddling blocks powered from two separate power packs.  When properly phased all power packs will source the main pulse at the same time, ie on the same half cycle of the AC powerline. 

[jbrock27]

Thank you.  The schematic is better, but I was hoping for some pics of the guts of the power pack.  Had you taken any of the work on it or no Glen?

[zeeglen]

but I was hoping for some pics of the guts of the power pack.  Had you taken any of the work on it or no Glen?

No, it was pretty straightforward, but I still have the cheater screwdriver and the power pack is around here somewhere.  Will get some photos this weekend, and now that I learned how to use photobucket will post them.

[jbrock27]

Thanks much for your efforts and help!

[zeeglen]

Thanks much for your efforts and help! :)

Here are the photos you asked for, these are better for those who wish to fix their own MRC1370 power packs.  Don't know if MRC would be willing to correct this manufacturing flaw on existing units, but one could ask them.  I approached MRC about this 10 years ago, they ignored the problem.  I guess, like Volkswagon and their Diesel emissions, they figured no one would notice.



Above is the tool to undo the 'security' screws.  All it takes is a needle file to cut the slot into a regular screwdriver. 
BE SURE TO UNPLUG THE POWER PACK FROM THE AC OUTLET BEFORE DIS-ASSEMBLING THE CASE!



Above:  Although not necessary, if you take a defective unit apart enough to lift out the printed circuit board (PCB) you will see an empty component location labelled R1.  This is a little to the left of center.  You have to pry up the heatsink (the flat metal plate) to make the external knob slip off the shaft of the speed control, then unscrew the large power transistor from the heatsink.  Do NOT remove the white thermal grease; this is needed to transfer heat from the transistor to the heatsink.



It is not necessary to remove the PCB to install the fix on the solder side of the PCB which is accessible as soon as the 4 screws holding the box together are removed.  The absence of R1 can be seen by the lack of wires protruding from the solder joints at the empty R1 location.  Solder in a new resistor as shown.  Anything between 5000 and 10000 ohms will work.  Be sure to use insulating sleeving on the resistor wires so they do not short circuit to anything else on the PCB.  The resistor wire soldered at top center of the photo can connect to either of the pads (but not both at the same time!) to which the red transformer wires are connected.  The choice of which pad is determined by the desired phasing as discussed in earlier posts.  Only matters if you run a train over blocks powered by more than one power pack.

You can see the fix is quite simple.  So why could MRC not have done this during manufacture?

[jbrock27]

Awesome Glen!  Thank you.

I made up one of those screw drivers a few years ago to open up a Railpower 1300.  Had to fix a stripped AC terminal screw.  Even though I was able to fix that, in the process, I messed up the DC control.  Ordered a pack of transistors from China and a pot from Mouser, but could not repair it.  At that point, it was not worth further investment of capital and relegated it to use of the AC terminals for switch motors. 

[zeeglen]

Awesome Glen!  Thank you.

You are welcome jbrock27.  Glad to help when I can.

I am curious as to whether MRC ever corrected this defect.  I see they are still selling the MRC1370.  It would be interesting for owners of these units who are reading this to open them up and see, and add the fix while opened if desired.  I emailed MRC asking, but based on their prior lack of response to my queries I doubt if I will hear from them.

Also those who do install the fix to report on the starting and slow speed running improvements.  I know this made a huge difference for the MTL Z Scale F7.

[jbrock27]

Don't have a answer why they have not address it.  Acting like VW as you pointed out.  Maybe bc not enough "noise" generated about it and certainly no one is going to go the press with a hobby power pack issue, no that many souls would pay it any attention anyway.  It would not make 60 Minutes.